Gene expression heterogeneities in embryonic stem cell populations: origin and function

Stem and progenitor cells are populations of cells that retain the capacity to populate specific lineages and to transit this capacity through cell division. However, attempts to define markers for stem cells have met with limited success. Here we consider whether this limited success reflects an intrinsic requirement for heterogeneity with stem cell populations. We focus on Embryonic Stem (ES) cells, in vitro derived cell lines from the early embryo that are considered both pluripotent (able to generate all the lineages of the future embryo) and indefinitely self renewing. We examine the relevance of recently reported heterogeneities in ES cells and whether these heterogeneities themselves are inherent requirements of functional potency and self renewal.     

Furfural production from xylose using sulfonic ion-exchange resins (Amberlyst) and simultaneous stripping with nitrogen

The aim of this work deals with the development of new approaches to the production of furfural from xylose. It combines relatively cheap heterogeneous catalysts (Amberlyst 70) with simultaneous furfural stripping using nitrogen under semi-batch conditions. Nitrogen, compared to steam, does not dilute the vapor phase stream when condensed. This system allowed stripping 65% of the furfural converted from xylose and almost 100% of selectivity in the condensate. Moreover, high initial xylose loadings led to the formation of two water-furfural phases, which could reduce further purification costs. Constant liquid-vapor equilibrium along stripping could be maintained for different xylose loadings. The modeling of the experimental data was carried out in order to obtain a liquid-vapor mass-transfer coefficient. This value could be used for future studies under steady-state continuous conditions in similar reaction-systems.     

Chronic intermittent hypoxia-induced vascular enlargement and VEGF upregulation in the rat carotid body is not prevented by antioxidant treatment

Chronic intermittent hypoxia (CIH), a characteristic of sleep obstructive apnea, enhances carotid body (CB) chemosensory responses to hypoxia, but its consequences on CB vascular area and VEGF expression are unknown. Accordingly, we studied the effect of CIH on CB volume, glomus cell numbers, blood vessel diameter and number, and VEGF immunoreactivity (VEGF-ir) in male Sprague-Dawley rats exposed to 5% O(2), 12 times/h for 8 h or sham condition for 21 days. We found that CIH did not modify the CB volume or the number of glomus cells but increased VEGF-ir and enlarged the vascular area by increasing the size of the blood vessels, whereas the number of the vessels was unchanged. Because oxidative stress plays an essential role in the CIH-induced carotid chemosensory potentiation, we tested whether antioxidant treatment with ascorbic acid may impede the vascular enlargement and the VEGF upregulation. Ascorbic acid, which prevents the CB chemosensory potentiation, failed to impede the vascular enlargement and the increased VEGF-ir. Thus present results suggest that the CB vascular enlargement induced by CIH is a direct effect of intermittent hypoxia and not secondary to the oxidative stress. Accordingly, the subsequent capillary changes may be secondary to the mechanisms involved in the neural chemosensory plasticity induced by intermittent hypoxia.     

The hylEfm gene in pHylEfm of Enterococcus faecium is not required in pathogenesis of murine peritonitis

Background  

Plasmids containing hyl _Efm (pHyl_Efm) were previously shown to increase gastrointestinal colonization and lethality of Enterococcus faecium in experimental peritonitis. The hyl _Efm gene, predicting a glycosyl hydrolase, has been considered as a virulence determinant of hospital-associated E. faecium, although its direct contribution to virulence has not been investigated. Here, we constructed mutants of the hyl _Efm -region and we evaluated their effect on virulence using a murine peritonitis model.     

Viral genome segmentation can result from a trade-off between genetic content and particle stability

The evolutionary benefit of viral genome segmentation is a classical, yet unsolved question in evolutionary biology and RNA genetics. Theoretical studies anticipated that replication of shorter RNA segments could provide a replicative advantage over standard size genomes. However, this question has remained elusive to experimentalists because of the lack of a proper viral model system. Here we present a study with a stable segmented bipartite RNA virus and its ancestor non-segmented counterpart, in an identical genomic nucleotide sequence context. Results of RNA replication, protein expression, competition experiments, and inactivation of infectious particles point to a non-replicative trait, the particle stability, as the main driver of fitness gain of segmented genomes. Accordingly, measurements of the volume occupation of the genome inside viral capsids indicate that packaging shorter genomes involves a relaxation of the packaging density that is energetically favourable. The empirical observations are used to design a computational model that predicts the existence of a critical multiplicity of infection for domination of segmented over standard types. Our experiments suggest that viral segmented genomes may have arisen as a molecular solution for the trade-off between genome length and particle stability. Genome segmentation allows maximizing the genetic content without the detrimental effect in stability derived from incresing genome length.     

Pyrrolidon carboxypeptidase activities in the hypothalamus-pituitary-thyroid and hypothalamus-pituitary-ovary axes of rats with mammary gland cancer induced by N-methyl nitrosourea.

Pyrrolidon carboxypeptidase is an omega-peptidase that hydrolyses N-terminal pyroglutamyl residues from biologically active peptides such as gonadotropin-releasing and thyrotrophin-releasing hormones. We previously described a decrease in both rat and human pyrrolidon carboxypeptidase activity with breast cancer, suggesting that gonadotropin-releasing hormone may be an important local intracrine, autocrine and/or paracrine hormonal factor in the pathogenesis of breast cancer while playing a role in the tumoral process. However, the other susceptible substrate of pyrrolidon carboxypeptidase, thyrotrophin-releasing hormone, may also be modified with breast cancer, supporting an association between breast cancer and thyroid disorders. The present work analyses soluble and membrane-bound pyrrolidon carboxypeptidase activities in the hypothalamus-pituitary-thyroid and hypothalamus-pituitary-ovary axes in N-methyl nitrosourea-induced breast cancer in rats. Our aim was to determine the possible relationship between gonadotropin-releasing hormone and thyrotrophin-releasing hormone regulation through pyrrolidon carboxypeptidase activity. We propose that pyrrolidon carboxypeptidase activity dysregulation at various local and systemic levels may participate in the initiation, promotion and progression of breast cancer induced in rat by N-methyl nitrosourea through the increase in gonadotropin-releasing hormone. Since pyrrolidon carboxypeptidase activity also acts on thyrotrophin-releasing hormone, the dysregulation of this enzyme's activity could indirectly affect hypothalamus-pituitary-thyroid axis function, and thus potentially represent a link between the diseases of thyroid and breast cancer.     

{Omega}-3 and {omega}-6 polyunsaturated fatty acids block HERG channels

Dietary polyunsaturated fatty acids (PUFAs) have been reported to exhibit antiarrhythmic properties, which have been attributed to their availability to modulate Na⁺, Ca²⁺, and several K⁺ channels. However, their effects on human ether-a-go-go-related gene (HERG) channels are unknown. In this study we have analyzed the effects of arachidonic acid (AA, -6) and docosahexaenoic acid (DHA, -3) on HERG channels stably expressed in Chinese hamster ovary cells by using the whole cell patch-clamp technique. At 10 µM, AA and DHA blocked HERG channels, at the end of 5-s pulses to –10 mV, to a similar extent (37.7 ± 2.4% vs. 50.2 ± 8.1%, n = 7–10, P > 0.05). 5,6,11,14-Eicosatetrayenoic acid, a nonmetabolizable AA analog, induced effects similar to those of AA on HERG current. Both PUFAs shifted the midpoint of activation curves of HERG channels by –5.1 ± 1.8 mV (n = 10, P < 0.05) and –11.2 ± 1.1 mV (n = 7, P < 0.01). Also, AA and DHA shifted the midpoint of inactivation curves by +12.0 ± 3.9 mV (n = 4; P < 0.05) and +15.8 ± 4.3 mV (n = 4; P < 0.05), respectively. DHA and AA accelerated the deactivation kinetics and slowed the inactivation kinetics at potentials positive to +40 mV. Block induced by DHA, but not that produced by AA, was higher when measured after applying a pulse to –120 mV (IO). Finally, both AA and DHA induced a use-dependent inhibition of HERG channels. In summary, block induced by AA and DHA was time, voltage, and use dependent. The results obtained suggest that both PUFAs bind preferentially to the open state of the channel, although an interaction with inactivated HERG channels cannot be ruled out for AA. K⁺ channel; membrane currents; ion channels; arrhythmia; antiarrhythmics     

Hybrid incompatibility is consistent with a hybrid origin of Heliconius heurippa Hewitson from its close relatives, Heliconius cydno Doubleday and Heliconius melpomene Linnaeus

Abstract Shared ancestral variation and introgression complicates the reconstruction of phylogenetic relationships among closely related taxa. Here we use overall genomic compatibility as an alternative estimate of species relationships in a group where divergence is rapid and genetic exchange is common. Heliconius heurippa, a butterfly species endemic to Colombia, has a colour pattern genetically intermediate between H. cydno and H. melpomene: its hindwing is nearly indistinguishable from that of H. melpomene and its forewing band is an intermediate phenotype between both species. This observation has lead to the suggestion that the pattern of H. heurippa arose through hybridization. We present a genetic analysis of hybrid compatibility in crosses between the three taxa. Heliconius heurippa x H. cydno and female H. melpomene x male H. heurippa yield fertile and viable F1 hybrids, but male H. melpomene x female H. heurippa crosses yield sterile F1 females. In contrast, Haldane's rule has previously been detected between H. melpomene and H cydno in both directions. Therefore, H. heurippa is most closely related to H. cydno, with some evidence for introgression of genes from H. melpomene. The results are compatible with the hypothesis of a hybrid origin for H. heurippa. In addition, backcrosses using F1 hybrid males provide evidence for a large Z(X)-chromosome effect on sterility and for recessive autosomal sterility factors as predicted by Dominance Theory.     

Phylogenetic relationships of honey bees (Hymenoptera:Apinae:Apini) inferred from nuclear and mitochondrial DNA sequence data

Two different genomic regions (ND2 mitochondrial gene and EF1-alpha intron) were PCR amplified, cloned and sequenced for the ten known honey bee species collected within their natural range distribution. DNA sequences were analyzed using parsimony, distance and maximum likelihood methods to investigate phylogenetic relationships within Apis. The phylogenetic analyses strongly supported the basic topology recoverable from morphometric analysis, grouping the honey bees into three major clusters: giant bees (A. dorsata, A. binghami, and A. laboriosa), dwarf bees (A. andreniformis and A. florea), and cavity-nesting bees (A. mellifera, A. cerana, A. koschevnikovi, A. nuluensis, and A. nigrocincta). However, the clade of Asian cavity-nesting bees included paraphyletic taxa. Exemplars of Apis cerana collected from divergent portions of its range were less related to each other than were sympatric A. cerana, A. nuluensis, and A. nigrocincta taxa. Nucleotide sequence divergence between allopatrically distributed western (A. mellifera) and eastern (A. cerana, A. koschevnikovi, A. nigrocincta, and A. nuluensis) cavity-nesting species, around 18% for the mitochondrial gene and 10-15% for the nuclear intron, suggested an earlier divergence for these groups than previously estimated from morphometric and behavioral studies. This latter finding neccessitates reevaluation of the hypothesized origin of extant European, African, and west Asian Apis mellifera. Sequence divergence between A. laboriosa and A. dorsata was consistent with behavioral data and supports the species status of A. laboriosa.     

Mitochondria permeabilization by a novel polycation peptide BTM-P1

Bacillus thuringiensis subsp. medellin is known to produce the Cry11Bb protein of 94 kDa, which is toxic for mosquito larvae due to permeabilization of the plasma membrane of midgut epithelial cells. Earlier we found that a 2.8-kDa novel peptide BTM-P1, which was artificially synthesized taking into account the primary structure of Cry11Bb endotoxin, is active against several species of bacteria. In this work we show that BTM-P1 induces cyclosporin A-insensitive swelling of rat liver mitochondria in various salt solutions but not in the sucrose medium. Inorganic phosphate and Ca(2+) significantly increased this effect of the peptide. The uncoupling action of BTM-P1 on oxidative phosphorylation was stronger in the potassium-containing media and correlated with a decrease of the inner membrane potential of mitochondria. In isotonic KNO(3), KCl, or NH(4)NO(3) media, a complete drop of the inner membrane potential was observed at 1-2 microg/ml of the peptide. The peptide-induced swelling was increased by energization of mitochondria in the potassium-containing media, but it was inhibited in the NaNO(3), NH(4)NO(3), and Tris-NO(3) media. All mitochondrial effects of the peptide were completely prevented by adding a single N-terminal tryptophan residue to the peptide sequence. We suggest a mechanism of membrane permeabilization that includes a transmembrane- and surface potential-dependent insertion of the polycation peptide into the lipid bilayer and its oligomerization leading to formation of ion channels and also to the mitochondrial permeability transition pore opening in a cyclosporin A-insensitive manner.